PAINTSTRUCT is not being filled out.

[Gavin-Williams]

The following code is producing an empty rect in the rcPaint field.

     PAINTSTRUCT paint;
     HDC dc = BeginPaint(Handle, &paint);

This also doesn't give a valid rect...

case WM_PAINT:
    {
        HDC dc = BeginPaint(Handle, out PAINTSTRUCT ps);

        int x = ps.rcPaint.left;
        int y = ps.rcPaint.top;
        int w = ps.rcPaint.right - ps.rcPaint.left;
        int h = ps.rcPaint.bottom - ps.rcPaint.top;

        Debug.WriteLine(w + "," + h);

        PatBlt(dc, x, y, w, h, ROP_CODE.WHITENESS); 
        EndPaint(Handle, in ps);
    }
    break;

[Gavin-Williams]

WINDOW_EX_STYLE.WS_EX_NOREDIRECTIONBITMAP was blocking rendering.

[AArnott]

I'm not familiar with the API to know for sure-- are you saying it was an error in your code and you're now unblocked?